Boosting aqueous non-flow zinc-bromine batteries with a two-dimensional metal-organic framework host: an adsorption-catalysis approach

Abstract

Aqueous non-flow zinc-bromine batteries (NF-ZBBs) offer low fabrication cost, good safety, and a large capacity, making them appealing energy storage systems. However, the performance of bromine conversion hosts is substantially hampered by the polybromide shuttle effect and sluggish redox reactions. In this study, we develop a high-performance aqueous NF-ZBB employing a two-dimensional conjugated nickel polyphthalocyanine (NiPPc) as an adsorption-catalysis cathode host. This innovative design tackles the critical issues of shuttle effect, low bromine utilization, and low discharge voltage in existing NF-ZBBs. Both experimental measurements and theoretical simulations reveal that the atomically dispersed Ni-N<inf>4</inf> sites in NiPPc act as effective sites for bromine redox reactions while exhibiting strong polarity for efficient adsorption of bromine and polybromides. This synergistic mechanism significantly enhances the overall full-cell electrochemical performance. The as-fabricated NF-ZBB showcases a large specific capacity of 265 mA h g⁻¹ at 2 A g⁻¹ with a high discharge voltage plateau of 1.82 V, approaching the theoretical value. It scores 240 mA h g⁻¹ even at 5 A g⁻¹ and retains ∼95% of this capacity after 3000 charge-discharge cycles. The NiPPc host with its unique adsorption-catalysis mechanism overcomes the limitations in conventional NF-ZBBs, emerging as a promising candidate for constructing high-performance aqueous batteries.